1. Field of the Invention
This invention relates to ion sources and is directed more particularly to a high current density ion source suitable for heating plasmas in controlled thermonuclear reaction experiments. Ion source modules which produce ion beams at 40 kv and ion current densities of 0.5A/cm.sup.2 have advanced to a rather sophisticated state of development. However, in the future, fusion test reactors will require multimegawatt neutral beams, each comprising a multiplicity of ion source modules. These modules will be exposed to the radioactive environment of the fusion reactor. Thus, highly reliable ion sources operating at high duty cycles will be required in order to expedite and simplify remote maintenance, handling and adjustment. In order to satisfy the neutral injection requirements for high beam currents, discharge currents ranging from 10 to 40 times the beam current will be required.
2. Prior Art
Prior art ion sources for neutral injection achieve the necessary discharge current by employing a relatively large number of filament cathodes which operate at temperatures approaching 3000.degree. K. The lift of such cathodes is limited by high thermal stress, sublimation and ion sputtering. Furthermore, heat radiated from the filament may cause undesirable thermal loads on critical components such as the ion optics.
Hollow cathodes have been used for ion thrusters and in inert gas ion sources.